In the sticky situation that the artists would have a problem with you using these images, then yes things could get messy. And if these images were ever shipped with tf2 in any way, then things get legally messy. It's always best to ask permission first. Deviant art isn't a free cache of images for anyone to use as they please--although that's fundamentally ignored and misunderstood.

There's no reason to take this down, but if you want these to be made into images, you should ask for permission first, it's always safest to just ask first.

Heavy Weapons Officer 1 and 2 on deviantart.com are cleared to use. The Heavy with Natascha should be fine because it was a picture from The Heavy Update which Valve released. As for the communist picture of Lenin and Stalin, I have not cleared that one to be used for now.

Edit: It would be great if someone could make the Natascha Heavy picture black and white.

"If the author of this work was subjected to repression and rehabilitated posthumously, countdown of copyright protection began not from the death date, but from the rehabilitation date. If the work was first published posthumously, the copyright term is counted from the date of that first publication, unless the author was later rehabilitated, in which case it runs again from that later rehabilitation date."